The present invention relates to fluid displacement apparatus and more particularly to an improved scroll-type machine especially adapted for compressing gaseous fluids and a method of manufacture thereof.
A class of machines exists in the art generally known as "scroll" apparatus for the displacement of various types of fluids. Such apparatus may be configured as an expander, a displacement engine, a pump, a compressor, etc., and many features of the present invention are applicable to any one of these machines. For purposes of illustration, however, the disclosed embodiments are in the form of a gaseous fluid compressor.
Generally speaking, a scroll apparatus comprises two spiral scroll wraps of similar configuration each mounted on a separate end plate to define a scroll member. The two scroll members are interfitted together with one of the scroll wraps being rotationally displaced 180.degree. from the other. The apparatus operates by orbiting one scroll member (the "orbiting scroll") with respect to the other scroll member (the "fixed scroll") to make moving line contacts between the flanks of the respective wraps defining moving isolated crescent-shaped pockets of fluid. The spirals are commonly formed as involutes of a circle, and ideally there is no relative rotation between the scroll members during operation, i.e., the motion is purely curvilinear translation (i.e. no rotation of any line in the body). The fluid pockets carry the fluid to be handled from a first zone in the scroll apparatus where a fluid inlet is provided, to a second zone in the apparatus where a fluid outlet is provided. The volume of a sealed pocket changes as it moves from the first zone to the second zone. At any one instant in time there will be at least one pair of sealed pockets, and when there are several pairs of sealed pockets at one time, each pair will have different volumes. In a compressor the second zone is at a higher pressure than the first zone and is physically located centrally in the apparatus, the first zone being located at the outer periphery of the apparatus.
Two types of contacts define the fluid pockets formed between the scroll members: axially extending tangential line contacts between the spiral faces of the wraps caused by radial forces ("flank sealing"), and area contacts caused by axial forces between the plane edge surfaces (the "tips") of each wrap and the opposite end plate ("tip sealing"). For high efficiency, good sealing must be achieved for both types of contacts, however, the present invention is primarily concerned with flank sealing. In a conventional scroll compressor (i.e. one in which the wraps are involutes of a circle) good flank sealing requires that there be no relative rotation between the scrolls.
Scroll devices are generally described in any early patent to Creux, U.S. Pat. No. 801,182. Among subsequent representative patents which disclose scroll compressors and pumps are U.S. Pat. Nos. 1,376,291, 2,475,247, 2,494,100, 2,809,779, 2,841,089, 3,560,119, 3,600,114, 3,802,809, 3,817,644, 3,884,599, 4,141,677, 4,300,875, 4,304,535 and 4,357,132.
The concept at a scroll-type apparatus has thus been known for some time and has been recognized as having distinct advantages. For example, scroll machines have high isentropic and volumetric efficiency, and hence are relatively small and lightweight for a given capacity. They are quieter and more vibration free than many compressors because they do not use large reciprocating parts (e.g. pistons, connecting rods, etc.), and because all fluid flow is in one direction with simultaneous compression in plural opposed pockets there are less pressure-created vibrations. Such machines also tend to have high reliability and durability because of the relative few moving parts utilized, the relative low velocity of movement between the scrolls, and an inherent forgiveness to fluid contamination. In spite of this, however, it is believed that the reason use of scroll machines of the prior art has not hitherto become wide spread is because of the difficulty of manufacturing such machines, as well as inherent sealing and unusual wearing problems.
One of the more difficult areas of design in a scroll machine concerns the technique used for preventing relative angular movement between the scrolls as they orbit with respect to one another. One of the more popular approaches resides in the use of an Oldham coupling operative between the orbiting scroll and a fixed portion of the apparatus. An Oldham coupling typically comprises an Oldham ring and two sets of key members or slider blocks. The Oldham ring is formed on one side thereof with grooves which are at right angles to a similar grooves formed on the other side thereof. One set of key members is connected to a surface of the orbiting scroll and is disposed in the grooves on one side of the Oldham ring, while the other set of key members is fixed to either the fixed scroll or the machine housing and is disposed in the grooves on the other side of the Oldham ring. The Oldham ring reciprocates in a motion parallel to the grooves containing the set of key members fixed to the fixed scroll or housing. The Oldham coupling thus acts as a means for controlling (i.e. preventing) angular rotation of the orbiting scroll relative to the fixed scroll, a concept that is believed to be essential to the successful functioning of a conventional scroll apparatus. U.S. Pat. No. 4,121,438 shows a machine of this construction.
Unfortunately, a scroll apparatus utilizing an Oldham coupling possesses several assembly, operational, and maintenance disadvantages, primarily due to the large number of parts that make up the coupling. This large number of parts increases material, manufacturing, and assembly cost. The slider blocks or key members in an Oldham coupling are also all sliding within the grooves on the Oldham ring, thus presenting lubrication and wearing problems. The reciprocating ring is also inherently impossible to balance.
There are other known devices for controlling relative rotation of the scrolls, such as the use of multiple drives rotating both scrolls about different centers, and like concepts; however, because of their complexity these devices also have many of the undesirable features of the Oldham coupling.
The present invention approaches the problem from a different direction. The basic concept of this invention resides in the use of a very simple orbiting scroll rotation controlling device which does not eliminate relative rotation, but simply controls it at a relatively small magnitude, in combination with techniques for easily modifying the contour of the scroll wraps to accommodate the limited relative rotation of the scrolls which occurs, in order to maintain flank sealing contact between the wraps. Three different versions of the rotation controlling device are disclosed, each being a simple linkage operatively connected between the orbiting scroll and a fixed portion of the compressor. Two embodiments are four-bar linkages and two additional embodiments are crank and slider arrangements. All versions couple the orbiting and fixed scrolls in a predetermined angular relationship in all relative positions as the orbiting scroll orbits with respect to the fixed scroll.
The orbiting scroll rotation controlling linkage of the present invention overcomes the aforesaid disadvantages of known techniques for accomplishing this function. Because it has fewer parts, it is less expensive to manufacture and is much easier to assemble. Lubrication problems are also reduced to a minimum because there are fewer connections and in one embodiment because the connections are entirely pivotal, rather than sliding. The anti-rotation member also contains no reciprocating ring.
In order to accommodate for the slight degree of rotation of the orbiting scroll, the present invention utilizes either one of two unique techniques for modifying the scroll wrap contours. Both of them are very easy to implement and provide highly efficient flank sealing (one of them provides theoretically perfect flank sealings) when used in combination with the aforesaid linkage arrangements. A novel wrap machining method is also provided.
The compressor of the present invention also embodies improved drive means for orbiting the scroll which is compact, as well as being simple to manufacture and assemble. This drive means, two embodiments of which are disclosed, provides the necessary contact between the scroll wraps to have efficient wrap sealing while at the same time provides an automatic unloading function in the event slugging or the like occurs. Should a non-compressible fluid be sucked into the compressor the orbiting radius of the orbiting scroll will automatically decrease to permit this fluid to escape between the scroll wraps to an area of less pressure (i.e. the scrolls will simply ride over any liquid). This function is accomplished without extra parts, such as valves or the like, and is very smooth in operation. The drive means is also nested within the upper crankshaft bearing, thereby reducing the axial height of the machine and lessening vibration.
The compressor of this invention also incorporates an improved thrust bearing arrangement to accommodate the axial loading of the orbiting scroll. The thrust bearing takes advantage of the inherent rotating movement of the orbiting scroll to create a squeeze film which provides the oil support for the bearing. The resulting bearing provides significantly less friction than conventional needle bearings and is much less subject to harmful wear than conventionally used balls. Ball-type thrust bearings, especially those with relatively small balls, have such high point loading that they tend to wear excessively. The present bearing is also relatively inexpensive, very simple in design and easy to manufacture and assemble.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.